From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753454AbYJ0AMA (ORCPT ); Sun, 26 Oct 2008 20:12:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751725AbYJ0ALv (ORCPT ); Sun, 26 Oct 2008 20:11:51 -0400 Received: from casper.infradead.org ([85.118.1.10]:44274 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751346AbYJ0ALu (ORCPT ); Sun, 26 Oct 2008 20:11:50 -0400 Date: Sun, 26 Oct 2008 17:12:10 -0700 From: Arjan van de Ven To: "Diego M. Vadell" Cc: Linux Kernel Subject: Re: PAT and MTRRs Message-ID: <20081026171210.7b3b096a@infradead.org> In-Reply-To: <200810262246.21807.dvadell@linuxclusters.com.ar> References: <200810262246.21807.dvadell@linuxclusters.com.ar> Organization: Intel X-Mailer: Claws Mail 3.5.0 (GTK+ 2.12.12; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 26 Oct 2008 22:46:21 -0100 "Diego M. Vadell" wrote: > Hello, > > I have 6 identical PCs (HPC cluster) with MTRR problems. In older > kernels, I had to use "mem=3300M", or else, I would get a very slowly > boot (as when you run out of MTRRs). > > So I thought that PAT would make this lack of MTRRs problem go > away, and upgraded to 2.6.26.6 and 2.6.27.2, but it didn't: I still > get (from dmesg) > > x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106 > WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing 704MB > of RAM. > > Most probably, I understood wrong. I read lwn.net's article [1] > about PAT several times, Documentation/x86/pat.txt , tried to use > mtrr_chunk_size= and mtrr_gran_size= in various combinations (as > discussed in this LKML thread [2]), but I still don't get it. > > So, what did I miss? Am I wrong thinking that PAT is a better MTRR > (wrt setting the cache type of the RAM)? > PAT can't make memory cachable that the MTRR's have as uncachable. What PAT *can* do is, within an MTRR, do fine grained mapping... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org